The present invention relates to internal combustion engines, and more particularly to an air filter for use upstream of a carburetor in an internal combustion engine such as would commonly be used in a lawn mower, snow blower, generator, or the like.
Internal combustion engines convert chemical energy to mechanical and electrical energy for wide varieties of applications. For example, a typical engine converts heat into motive power by burning a mixture of air and a flammable hydrocarbon, such as gasoline, in a cylinder having a moveable piston positioned therein. Linear motion of the piston rotates a crankshaft that transmits power to a rotor such as a connecting rod. The rate at which the piston moves up and down within the cylinder dictates the speed at which the crankshaft rotates, as regulated by a carburetor controlling the air-fuel mixture within the cylinder.
If dirt or dust or other contaminants are drawn into the engine as part of the air-fuel mixture generated by the carburetor, they become a part of the oil film between the engine""s moving parts and form an abrasive mixture that is very damaging to the engine. In order to remove solid impurities from an airstream and thus prevent them from entering the engine, an air filtration assembly is commonly positioned upstream of the carburetor in order to filter the air that is delivered to the air intake duct of the carburetor.
As known, many air filtration assemblies employ a filter element in the form of an annulus of porous filter paper that permits air to flow therethrough. As an indispensable adjunct of every internal combustion engine, the filter element must be periodically removed and either cleaned or replaced. The frequency with which this task must be performed depends, in substantial part, upon the environment in which the engine operates.
In some cases, such as in a lawn mower, the engine is partially or totally covered by a housing that is usually made of plastic or other non-conducting material. Typically, separate housings cover the air filtration system and cooling system. Additionally, baffles to direct the air to the engine intake are usually attached to the housings. Each of these housings and baffles require a fastening system, which increases part count and complexity of manufacture and assembly. Typically, the plurality of housings must be disassembled and reattached using tools. Moreover, the housings for the sub-assemblies are often nested beneath the main or other housings, such that multiple housings may have to be removed to access a single sub-assembly. Multiple housings and cumbersome fastening systems render servicing the engine and its sub-assemblies and systems difficult.
For example, a typical prior art filtration system 110, as depicted in FIGS. 1-A and 1-B, comprises an air cleaner case 112 having a covering top 114, a covering bottom 115, and a continuous sidewall 116 depending from the perimeter of the covering top 114 to the perimeter of the covering bottom 115. In this system 110, an air filter 118 is detachably held in place by a plurality of threaded members 120 that extend up from the covering bottom 115 towards the covering top 114. The covering top 114 has a plurality of orifices 122 for receiving the threaded members 120 and being secured thereto via a fastener mechanism 124 such as a wing-nut. Each fastener mechanism 124 co-acts with a threaded member 120 to draw the covering top 114 and covering bottom 115 towards one another, thereby securing the air filter 118 in the case 112.
To ensure against unfiltered air being drawn into the carburetor, large first and second sealing surfaces 126A-B of the air filter 118 are typically provided for interfacing between the air filter 118 and both the covering top 114 and covering bottom 115. These sealing surfaces 126 are generally provided along the entire top and bottom of the filter 118. In addition, sealing gaskets 128 are frequently placed intermediate the fastener mechanism 124 and covering top 114 to prevent air from being drawn through the orifices 122 of the covering top 114.
The traditional air filtration system 110 thus requires large sealing surfaces 126 and gaskets 128 in order to prevent unfiltered air from being drawn into the engine. These parts 126, 128 demand close tolerances in order for the seals to be effective. Any misassembly, missing parts, slightly warped materials or other non-conformities can cause unfiltered air to enter the engine.
Moreover, to perform a filter change, the fastener mechanism 124 is loosened and removed; the gaskets 128 and covering top 114 are then removed; the air filter 118 is then removed and a new or cleaned filter 118 is inserted; the covering top 114 is repositioned and the threaded members 120 are realigned; and finally, each fastener mechanism 124 is resecured to each corresponding threaded member 120 in order to complete the inspection, replacement, or cleaning of the air filter 118.
As is evident from the foregoing, a need exists for an air filtration system having an air filter that is easier to replace than are the air filters of present design, require fewer parts, and decrease the amount of unfiltered air that is delivered to the air intake duct of the carburetor of an internal combustion engine.
Provided by this invention is an air filter for an internal combustion engine, the filter having a top wall, a sidewall depending from a perimeter of the top wall and including a filter material through which engine intake air flows, and a bottom wall attached to the sidewall and spaced apart from the top wall to form an integral housing that defines a cavity. An orifice extends through the bottom wall and receives the air intake duct of a carburetor in sealing and frictional engagement.
A general object of the invention is to provide a filtration system in which the air filter is easy to change, i.e., requires no tools. Accordingly, the old air filter is pulled free, and simple hand pressure is exerted to fit a new or cleaned filter over the air intake duct of the carburetor. In the preferred embodiment, a friction-fit is provided by the interior surface defined by the orifice, such that the interior surface decreases in cross-sectional area in the direction of the cavity. Preferably, the interior surface comprises a plurality of stepped diameters of a bottom wall material. Alternatively, the interior surface conically slopes inward towards the cavity. In yet another alternative embodiment, the interior surface comprises a plurality of ridges that encircle the air intake duct when the air filter is placed onto the engine.
Another object of this invention is to provide a good seal to prevent contaminants from entering the carburetor. The filter itself is an integral housing in which air can enter the cavity only through the filter material in the sidewall. The filter""s only seal is limited to the region of the friction-fit between the air intake tube and the surrounding interior surface formed by the orifice in the bottom wall.
The air filter forms part of an air filtration system in which a holding arm having a hook shaped distal end with a catch extends upward from a carburetor air intake platform in order to hold the filter in place. The catch is received in an indentation formed along a top surface of the top wall of the filter. The catch is disengaged by pulling a grip formed at the top of the holding arm, thus allowing easy removal and replacement of the filter.
The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown, by way of illustration, preferred and alternative embodiments of the invention.